Abstract
A semiconductor device structure and a manufacturing method thereof are provided. The semiconductor device structure includes a substrate, a semiconductor layer on the substrate, and a patterned dielectric layer disposed on the substrate and covered by the semiconductor layer. The patterned dielectric layer is configured to prevent components in the semiconductor layer from diffusing into the substrate. The semiconductor device structure also includes a first nitride semiconductor layer on the semiconductor layer and a second nitride semiconductor layer on the first nitride semiconductor layer. The band gap of the second nitride semiconductor layer is larger than the band gap of the first nitride semiconductor layer.